1. Field of The Invention
This invention relates to a method for fabricating an (Al.sub.x Ga.sub.1-x)In.sub.1-y P semiconductor-based visible light laser device by molecular beam epitaxy.
2. Description of The Prior Art
Fabrication of semiconductor laser devices by molecular beam epitaxial (MBE) apparatus has been recently proposed. The fabrication using the MBE apparatus requires at least two MBE growth steps. These steps are described below.
In the first step, a first expitaxially grown structure including a lower clad layer, an active layer and an upper clad layer is built up on a semiconductive substrate. After the epitaxial growth, the substrate is withdrawn from a MBE chamber to an atmospheric environment. Then, a stripe groove is formed in the structure, for example, by a photo etching procedure. After removal of impurities, which have been attached during the photo etching procedure, from the substrate surface and also of an oxide film inevitably formed on the surface of the substrate by exposure to the air, a second MBE step is effected to form a second growth film on the grooved structure.
However, where the clad layer is made, for example, of (Al.sub.x Ga.sub.1-x).sub.0.5 In.sub.0.5 P wherein x is not smaller than 0.4, the impurities and oxide film as mentioned above are difficult to evaporate. In fact, such impurities and oxide film cannot be removed by an ordinary thermal treatment, such as thermal cleaning or thermal etching, in the MBE growth chamber. This presents the problems that there are produced crystal defects at the interface between the clad layer and the second growth layer formed in the subsequent step and that crystallinity of the second growth layer is degraded. More particularly, the high resistance layer is undesirably formed at or in the vicinity of the interface, so that the electric current may become difficult to pass or the high resistance layer may serve as a light absorption layer. Thus, it will be difficult to fabricate a semiconductor laser device which has good electric and optical properties.